Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · Electrical engineering and control panels

Safety extra-low voltage (SELV)

Also known as: SELV

German: Schutzkleinspannung (SELV)

In electrical safety, safety extra-low voltage (SELV) is an extra-low voltage system that is electrically separated from earth and from other systems in such a way that a single fault cannot cause the risk of electric shock.

  • Control panels

In one sentence

SELV is an extra-low voltage circuit separated from earth and other systems so a single fault can't cause electric shock.

Example

A handheld test pendant is supplied from a SELV circuit, so the operator can't receive a dangerous shock even if the cable insulation is damaged.

How it applies

  • Engineering: SELV requires an extra-low voltage source with protective separation (such as a safety isolating transformer) and no connection to earth or to protective conductors. Keep SELV circuits separated from all other circuits along their route.
  • Installation: Connecting 0 V to earth, which is common practice in control cabinets, turns a SELV circuit into PELV. Check the design intent before earthing.
  • Documentation: Mark SELV circuits in the circuit diagram and describe the conditions for keeping them SELV in the installation instructions. Don't call every 24 V circuit "SELV"; most machine control circuits are PELV.

SELV vs. PELV

SELV is isolated from earth; Protective extra-low voltage (PELV) may be earthed. Both use protective separation from higher voltages, but the requirements and protection concept differ.

By knowledge.aitechdoc.world · Published September 26, 2026 · Last reviewed

Source: IEC 60364-4-41, Low-voltage electrical installations — Part 4-41: Protection for safety — Protection against electric shock

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Knowledge and are not part of any standard.

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